Mononuclear, dinuclear, hexanuclear, and one-dimensional polymeric silver complexes having ligand-supported and unsupported argentophilic interactions stabilized by pincer-like 2,6-bis(5-pyrazolyl)pyridine ligands

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Abstract
The mononuclear complexes [Ag(H2L1)(Py)2](NO3)·H2O (1, H2L1 = 2,6-bis(5-methyl-1H-pyrazol-3-yl)pyridine) and [Ag(NO3)(L2)] (2, L2 = 2,6-bis(5-methyl-1-isopropyl-1H-pyrazol-3-yl)pyridine), dinuclear complex [Ag2(H2L3)2(HL4)2] (3, H2L3 = 2,6-bis(5-phenyl-1H-pyrazol-3-yl)pyridine, HL4 = 6-(5-phenyl-1H-pyrazolyl-3-yl)picolinate), one-dimensional polymer {[Ag2(H2L1)2](NO3)2·H2O}n (4), and hexanuclear clusters [Ag6(HL1)4](X)2 (X = NO3 −, 5; BF4 −, 6; ClO4 −, 7) stabilized by pincer-like bispyrazolyl ligands have been prepared and characterized using 1H NMR spectroscopy, elemental analysis, IR spectroscopy, luminescence spectroscopy and X-ray diffraction. In complex 3, there is a ligand unsupported Ag–Ag bond between the two silver atoms. Complex 4 displays a one-dimensional polymer consisting of an infinite Ag–Ag chain and every two adjacent silver ions are bridged by an H2L1 ligand. Complexes 5 and 7 have the same Ag6 cores in which six silver atoms are held together by four HL1 and five Ag–Ag bonds, while complex 6 was held together by six Ag–Ag bonds. The silver–silver distances in these complexes are found in the range of 2.874(1)–3.333(2) Å for ligand supported, and 3.040(1) Å for ligand unsupported Ag–Ag bonds, respectively. Complexes 3–7 are strongly luminescent due to either intraligand or metal–ligand charge transfer processes.

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